Sensitivity analysis (SA) of model parameters is of great importance for understanding, development, and application of models. However, the influence of snow microstructure variability on snow water ...equivalent retrieval from passive microwave measurements is still unclear. This article explores the parameter sensitivity of the microwave emission model of layered snowpacks (MEMLS) with improved born approximation (IBA) by using a quantitative global SA method, the extended Fourier amplitude sensitivity test (EFAST) algorithm. A deep analysis is conducted, including the sensitivity of passive microwave emission to snow parameters, the sensitivity variation analysis for different snow conditions, and the temporal properties of the parameter sensitivity. The results show the exponential correlation length, snow depth, and snow density are the three most sensitive parameters for snow without salt in the MEMLS model for the brightness temperature gradient at 18.7 and 36.5 GHz. For snow with a small salt content, the exponential correlation length, snow depth, snow temperature, and snow density are the four most sensitive parameters. Second, snow parameter variability highly affects the microwave radiation. The sensitivity values of microwave brightness temperature to snow depth gradually increase when the exponential correlation length is less than 0.25 mm and then slightly decreases with the increase of exponential correlation length and decreases along with the increase of snow density. Finally, our analysis highlights the importance to include the snow density, especially for deep snow depth, in the combination of sensitive factors in future multiparameter retrievals.
A photonic-assisted multi-functional radar system for simultaneous distance and velocity measurement and high-resolution microwave imaging is proposed and experimentally demonstrated by using a ...composite transmitted microwave signal of a single-chirped linearly frequency-modulated (LFM) signal and a single-tone microwave signal. In the system, the transmitted signal is generated via photonic frequency up-conversion based on a single integrated dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM), while the echo signals scattered from the target are de-chirped to two low-frequency signals using a microwave photonic frequency mixer. By using the two low-frequency de-chirped signals, the real-time distance and radial velocity of the moving target can be measured accurately according to the round-trip time of the echo signal and its Doppler frequency shift. Compared with the previously reported distance and velocity measurement methods, where two LFM signals with opposite chirps are used, these parameters can be obtained using only a single-chirped LFM signal and a single-tone microwave signal. Meanwhile, high-resolution inverse synthetic aperture radar (ISAR) imaging can also be realized using ISAR imaging algorithm. An experiment is performed to verify the proposed multi-functional microwave photonic radar system. An up-chirped LFM signal from 8.5 to 12.5 GHz and an 8.0 GHz single-tone microwave signal are used as the transmitted signal. The results show that the absolute measurement errors of distance and radial velocity are less than 5.9 cm and 2.8 cm/s, respectively. ISAR imaging results are also demonstrated, which proves the high-resolution and real-time ISAR imaging ability of the proposed system.
Harvesting low-density ambient microwave power as an alternative power source for small ubiquitous wireless nodes has been proposed in recent papers discussing emerging technologies like the Internet ...of Things and Smart Cities. However, a literature review of the state-of-the-art Schottky diode based microwave rectifiers shows that a maximum efficiency has been reached for such devices operating in the low-power regime, as is the case for ambient microwave power-harvesters. This work examines the underlying physical mechanisms responsible for this RF-to-dc power conversion efficiency limitation, and explores a high I-V curvature backward tunnel diode to overcome this efficiency limitation. Measurements of the 2.4 GHz RF-to-dc power conversion efficiency at -40 dBm input power demonstrates that the backward tunnel diode outperforms the HSMS-285B Schottky diode by a factor of 10.5 and the Skyworks SMS7630 by a factor of 5.5 in a lossless matching network scenario. A prototype built using a new GSG probe embedded with a matching circuit showed a total power conversion efficiency of 3.8% for -40 dBm input power and 18.2% for -30 dBm input power at 2.35 GHz.
Editorial Pedro, Jose Carlos; Perregrini, Luca; Grimoldi, Laura ...
IEEE transactions on microwave theory and techniques,
2017-Jan., Letnik:
65, Številka:
1
Journal Article
Recenzirano
The IEEE Transactions on Microwave Theory and Techniques (MTT) is the premier journal for the dissemination of scientific results regarding the design and application of high-frequency devices, ...circuits, and systems. Covering all theoretical and practical aspects of radio-frequency technology for the last 63 years, it is regarded by the vast majority of researchers and engineers as the most convenient vehicle to publish a work worth sharing or to find a concept, tutorial, or technique worth knowing.
The microwave compressor of a new design forms high-power rectangular pulses of a spatial length exceeding several folds the longitudinal dimension of a storage cavity. Similar to the known ...compressor with the single-mode circular cavity, the new one has small overall dimensions due to making the cavity as a meander formed by parallel waveguide sections. The input coupler is the input port of the first section, and the output unit is the output port of the last section. Unlike the known compressor, the waveguide elements of the proposed one are oversized. Requirements for the design are determined and characteristics are estimated. Comparing with the analog compressor, the gain of the proposed one is greater by 7 dB. The processes of energy storing and extraction and the characteristics of the X-band compressor were analyzed by computer simulation. The compressor was tested experimentally, and the results were compared with the simulation data. It was shown that the microwave compressor with the oversized compact cavity worked similar to the analog compressor.
A novel approach to implementing instantaneous frequency measurement (IFM) based on an amplified fiber-optic recirculating delay loop and a broadband incoherent light source (ILS) is proposed, ...analyzed, and experimentally demonstrated. Since the semiconductor optical amplifier-based fiber-optic delay loop has an infinite impulse response that varies from a large positive value to negative infinity on a log scale, a unique relationship between the output power, and the frequency of the input continuous-wave (CW) microwave signal is established. Meanwhile, it is experimentally shown that the use of the ILS can greatly improve the stability of the proposed IFM system. When the input power of CW microwave signal is within the range of -7 dBm to -16 dBm, the measured errors remain within ±400 KHz over a frequency range of 6.94-6.958 GHz. The measurement error, the complexity and cost of the proposed IFM system can be considerably reduced by only using one ILS, one modulator, and one photodetector. Since the proposed IFM system has a capability of optical integration, it is theoretically estimated that the measurement range can be extended to 20 GHz with a measurement resolution of 1.36 dB/GHz.
Shielding ultracold molecules
Ultracold molecules hold promise for a wide range of exciting applications. However, such applications are currently hampered by the limited number of ultracold ...molecular ensembles that can be created and by their short lifetimes. Anderegg
et al
. used a microwave dressing field to tune the collisional properties of calcium monofluoride molecules trapped in optical tweezers. This approach allowed a sixfold suppression of inelastic trap-loss collisions. This scheme paves the way for the creation of a variety of long-lived ultracold molecular ensembles. —YS
Microwave shielding of inelastic collisions between CaF molecules is realized in 3D using optical tweezer traps.
Harnessing the potential wide-ranging quantum science applications of molecules will require control of their interactions. Here, we used microwave radiation to directly engineer and tune the interaction potentials between ultracold calcium monofluoride (CaF) molecules. By merging two optical tweezers, each containing a single molecule, we probed collisions in three dimensions. The correct combination of microwave frequency and power created an effective repulsive shield, which suppressed the inelastic loss rate by a factor of six, in agreement with theoretical calculations. The demonstrated microwave shielding shows a general route to the creation of long-lived, dense samples of ultracold polar molecules and evaporative cooling.
This paper presents an energy selective surface (ESS) for high-power microwave (HPM) protection in waveguide, which has a nonlinear transmission response and can adaptively react to the power ...intensity of an incident wave. A prototype of four unit cells loaded with p-i-n diodes is designed and fabricated in L -band. The nonlinear and adaptive transmission characteristics are demonstrated by the waveguide measurements both in the time domain and frequency domain. On condition of signal power below 35 dBm, the wave in the interested band can propagate through waveguide with a low insertion loss down to 1 dB; while on condition of signal power above 47 dBm, high power would render the ESS into a high-impedance surface, and the incident wave would be reflected and dissipated with a transmission coefficient of less than -10 dB, thereby providing the HPM protection ability. Furthermore, the subsequent simulations illustrate that the inserted ESS will not worsen the radiation patterns of the following horn antenna and the induced high-order modes in waveguide keep negligible values below -65 dB.
A novel four-port circulator is presented which uses an inline ferromagnetic element to allow for transmission or reflection depending on the sense of the incident circularly polarized wave. This ...configuration has been shown to reduce the dependency on ferrite anisotropy and support higher power, low rf loss, operation. An analytic analysis of this device is presented alongside corroborating cold test data of the first prototype. High-power operation was performed at 2.856 GHz, with input power levels up to 8 MW for <inline-formula> <tex-math notation="LaTeX">3.5~\mu \text{s} </tex-math></inline-formula> in a pressurized nitrogen environment. The results from this research not only demonstrate ability to eliminate the use of greenhouse insulators, such as SF 6 , but also provide conceptual groundwork for a new class of ultrahigh power (50 MW+) nonreciprocal networks including circulators, isolators, phase shifters, and rf switches.
A low-profile Substrate IntegratedWaveguide (SIW) cavity backed self-quadruplexing slot antenna supporting both microwave and mm-wave frequencies is proposed. Initially, a square SIW resonator is ...designed, and diagonally bisected into two half-mode resonators. A small portion of each section is assigned for mm-wave frequencies (28 and 30 GHz), and the remaining parts are adjusted to operate at microwave frequencies (4.8 GHz and 5.4 GHz). The microwave frequencies utilize the fundamental mode of the cavity and attain a maximum gain of 5.4 and 5.2 dBi at 4.8 and 5.4 GHz, respectively. The mm-wave resonators take advantage of higher order mode, resulting in a realized maximum gain of 8 and 8.7 dBi at 28 and 30 GHz. The simulated and measured results verified that at the mentioned frequencies, the reflection coefficients are below -20 dB, and the isolation among ports is better than 20 dB as well. Thus, it is asserted that the suggested antenna is a good candidate for 5G communication systems utilizing sub-6 GHz and mm-wave bands. This can be considered as the first self-quadruplexing antenna designed for both microwave and mm-wave frequencies.
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